The most common and most likely answer to this crossword clue is the 8 letter word CATALPAS
I've seen this crossword clue in Independent
C
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Buddy explains!
The straight part
We know that "flowering plants" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case flowering plants = catalpas.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CATALPAS mean?
CATALPAS noun- Any tree of the genus Catalpa, in the family Bignoniaceae. The two North American species, the southern catalpa, Catalpa bignonioides, and the northern catalpa, Catalpa speciosa — along with the yellow catalpa, Catalpa ovata, from China — are often planted as ornamentals because of their showy flowers and decorative bean pods, though others regard the bean pods as a nuisance.